Conventionally, a hot and cold water mixing valve has been used for controlling a temperature of a mixture of hot and cold water by biasing a movable valve member for changing a mixture ratio of hot water to cold water by means of a spring made of a shape memory alloy whose spring constant changes with temperature. Such a hot and cold water mixing valve is disclosed in Patent Document 1, for example.
Patent Document 1 discloses a hot and cold water mixing valve which uses a spring made of a shape memory alloy as a temperature sensitive actuator, and is arranged such that mixed water passes outside the spring made of the shape memory alloy. Further, Patent Document 1 discloses a structure where a seat surface part to which a generation load is applied is formed at one end of the spring made of the shape memory alloy and a movable valve member is moved according to a motion of the seat surface part.
Now, a structure of the above-mentioned conventional hot and cold water mixing valve will be described with reference to FIG. 1. A hot and cold water mixing apparatus W as shown is provided with a cylindrically formed casing 1, an adjustment screw 3 threadedly engaged with one end part of the casing 1, and a plug 12 threadedly engaged with the other end side of the casing 1.
A hot water inlet a and a cold water inlet b are opened axially in parallel at a side wall of the casing 1. A hot water inflow pipe 10 for conducting hot water and a cold water inflow pipe 11 for conducting cold water are connected to them. Further, the control valve member 2 formed in the shape of a cylinder or in the shape of a spool is movably fitted into the casing 1 in an axial direction. A conventional biasing member 4 which is supported by the adjustment screw 3 threadedly engaged with one end part of the casing 1 and has a fixed spring constant with respect to temperature is abutted against one axial end of the control valve member 2. Further, the temperature sensitive spring 5 which is supported by the plug 12 threadedly engaged with the other end side of the casing 1 and which is made of a metal or synthetic resin material whose spring constant changes with temperature is abutted against the other axial end of the control valve member 2. The control valve member 2 is held in a situation of being balanced between the temperature sensitive spring 5 and the above-mentioned biasing member 4.
The casing 1 has provided therein a mixing chamber 13 for mixing the hot water which flows in through the hot water inlet a with the cold water which flows in through the cold water inlet b, and a discharge room 14 for conducting a mixture of water mixed in the mixing chamber 13 to a mixed water outlet c provided for the casing 1. Further, the control valve member 2 has formed and provided therein a hot water valve 2a and a cold water valve 2b facing the hot water valve seat 10a and the cold water valve seat 10b which are formed and provided at mouth edges of the hot water inlet a and the cold water inlet b.
Thus, in a situation where it is set as a desired preset temperature by means of the adjustment screw 3, if a flow rate of the cold water which flows in decreases with decreasing hydraulic pressure etc. and the temperature of the mixed water in the mixing chamber 13 rises accordingly, then the temperature sensitive spring 5 which detects it may operate to increase the generation load. When the temperature sensitive spring 5 operates to increase the generation load, it pushes and contracts the biasing member 4 to move the control valve member 2 to the left, narrows a spacing between the hot water valve 2a and the hot water valve seat 10a to lower a valve lift of the hot water inlet a, reduces an inflow rate of the hot water to lower the temperature of the mixed water, and at the same time stabilizes the control valve member 2 in a position where the mixture ratio between the hot water and the cold water of the mixed water and the temperature of the mixed water are balanced.
Further, when the flow rate of the cold water which flows in increases with increasing hydraulic pressure etc. and the temperature of the mixed water in the mixing chamber 13 falls, the temperature sensitive spring 5 operates to reduce the generation load by its detection operation. When the temperature sensitive spring 5 operates to reduce the generation load, the biasing member 4 expands by the reduced load so as to move the control valve member 2 to the right, and narrows the spacing between the cold water valve 2b and the cold water valve seat 10b so as to lower a valve lift of the cold water inlet b and reduce the flow rate of the incoming cold water. In this way, the temperature of the mixed water which has fallen is raised so that the control valve member 2 is stabilized in the position where the mixture ratio of the hot water to the cold water and the temperature of the mixed water are balanced and the temperature of the discharging mixed water is held at the setup temperature.
Patent Document 1: Japanese Patent Application Publication No. 2006-307971